In the medical field, various types of body implantable leads are known and used. One type of commonly used implantable lead is an endocardial pacing lead.
Endocardial pacing leads are attached at their proximal end to an implantable pulse generator and at their distal end to the endocardium of a cardiac chamber. The distal end of an endocardial lead may engage the endocardium by either an active fixation mechanism or a passive fixation mechanism.
Active fixation mechanisms use a structure, such as helix or hook, to physically engage into or actively affix themselves onto the heart. Passive fixation mechanisms, such as a tine assembly, lodge or passively fix themselves to the heart.
A preferred means for introducing an endocardial lead into the heart is through a vein. Specifically, such a lead, called a transvenous lead, is introduced into and maneuvered through the vein so the distal end is positioned within the heart. Generally, passive fixation leads are introduced into the heart in this manner, in particular, because the interior of the ventricular contains trabeculae which are easily and sufficiently engaged by tines.
One difficulty which has been encountered with such a design occurs from the packaging and handling of the tined leads before they are introduced into the patient. In particular, because it is necessary for the lead to be constructed from a pliant bio-compatible material, such as silicone, pre-implantation handling has been found on occasion to cause the lead structure to be deformed. In particular, it has been found that on occasion the tine assembly can be stretched or elongated so as to partially cover the electrode at the distal end of the lead. A partially covered electrode does not have the same electrical properties as if it were not covered. This may affect lead performance and ultimately affect the performance of the implantable pulse generator.